❤️ 3.6 - 3.6.1 - 3.6.1.2 Receptors (A-level only)

Question 1

Receptors are specific. What does this mean?

Answer 1

They only detect one particular stimulus, e.g. light, pressure or glucose concentration.

Question 2

What are the two things receptors can be?

Answer 2

They can be cells (e.g. photoreceptors are receptor cells that connect to the nervous system).
They can be proteins on cell surface membranes (e.g. glucose receptors are proteins found in the cell membranes of some pancreatic cells).

Question 3

When a nervous system receptor is in its resting state (not being stimulated), what is there a difference in?

Answer 3

The charge between the inside and the outside of the cell. The difference is generated by ion pumps and ion channels.

Question 4

What does it mean if there is a difference in change between the inside and outside of the cell?

Answer 4

That there is a voltage across the membrane.

Question 5

What is voltage also known as?

Answer 5

Potential difference.

Question 6

What is the potential difference when a cell is at rest called?

Answer 6

Its resting potential.

Question 7

When a stimulus is detected, the cells membrane is excited, which causes the membrane to become more …

Answer 7

… permeable.

Question 8

If the cell membrane becomes more permeable, what does this mean? What does this cause?

Answer 8

More ions can move in and out of the cell. This alters the potential difference.

Question 9

What is the change in potential difference due to?

Answer 9

A stimulus and is called the generator potential.

Question 10

A bigger stimulus excites the membrane more, what does this cause?

Answer 10

A bigger movement of ions and a bigger change in potential difference - so a bigger generator potential is products.

Question 11

If the generator potential is big enough, what will it trigger?

Answer 11

An action potential.

Question 12

What is an action potential?

Answer 12

An electrical impulse along a neurone.

Question 13

An action potential is only triggered if the generator potential reaches a certain level called the what?

Answer 13

Threshold level.

Question 14

What is the strength of the stimulus measured by, as action potentials are all one size?

Answer 14

The frequency of action potentials (the number of action potentials triggered during a certain time period).

Question 15

What happens if the stimulus is too weak?

Answer 15

The generator potential won’t reach the threshold, so there is no action potential.

Question 16

What type of receptors are pacinian corpuscles in your skin?

Answer 16

Pressure receptors.

Question 17

What type of receptors are pacinian corpuscles?

Answer 17

Mechanoreceptors - they detect mechanical stimuli, e.g. pressure and vibrations. They are young in your skin.

Question 18

Where are the pressure receptors, pacinian corpuscles found?

Answer 18

In your skin.

Question 19

What type of neurone do pacinian corpuscles contain the end of? What is it wrapped in?

Answer 19

Sensory called the sensory nerve ending. It is wrapped in loads of layers of connective tissue called lamellae.

Question 20

What happens when a pacinian corpuscles is stimulated?

Answer 20

The lamellae become deformed and press on the sensory nerve ending.

Question 21

What happens when the lamellae on the sensory nerve ending become deformed?

Answer 21

The sensory neurone’s cell membrane stretched, deforming the stretch-mediated sodium ion channels. The channels open and sodium ions diffuse into the cell, creating a generator potential.

Question 22

What do pacinian corpuscles only respond to?

Answer 22

Mechanical stimuli.

Question 23

What are photoreceptors?

Answer 23

Light receptors in your eye.

Question 24

What does light enter the eye through?

Answer 24

The pupil.

Question 25

How is the amount of light that enters the eye through the pupil controlled?

Answer 25

By the muscles of the iris.

Question 26

Light rays are focused by the lens onto the ...

Answer 26

... retina - which lines the inside of the eye.

Question 27

What does the retina contain?

Answer 27

Photoreceptor cells - these detect light.

Question 28

What is the fovea?

Answer 28

An area of the retina where there are lots of photoreceptors.

Question 29

Where are nerve impulses from the photoreceptor cells carried from and to and by what?

Answer 29

From the retina to the brain by the optic nerve - which is a bundle of neurones.

Question 30

What is the blind spot?

Answer 30

Where the optic nerve leaves the eye.

Question 31

Why is the blind spot (where the optic nerve leaves the eye) not sensitive to light?

Answer 31

Because there are not any photoreceptor cells.

Question 32

What do photoreceptor cells convert light into?

Answer 32

An electrical impulse.

Question 33

What happens as light enters the eye?

Answer 33

- It hits the photoreceptors and is absorbed by light-sensitive optical pigments. - The light then bleaches the pigments which causes a chemical change and alters the membrane permeability to sodium ions. - A generator potential is therefore created and if it reaches the threshold,, a nerve impulse is sent along a bipolar neurone.

Question 34

What are bipolar neurones?

Answer 34

Neurones which connect photoreceptors to the optic nerve, which takes impulses to the brain.

Question 35

What two things does light pass straight through to get to the photoreceptor?

Answer 35

The optic nerve and the bipolar neurone.

Question 36

Name the two types of photoreceptors.

Answer 36

Rods and cones.

Question 38

Where are rods mainly found and where are cones found?

Answer 38

Rods are mainly found in the peripheral parts of the retina, and cones are found packed together in the fovea.

Question 39

What makes rods and cones sensitive to different wavelengths of light?

Answer 39

The different optical pigments they each have.

Question 40

What colour do both rods and cones each give information in?

Answer 40

Rods - black and white (monochromatic vision) Cones - colour (trichromatic vision)

Question 41

What are the 3 types of cones? What makes the 3 types of cones different from each other?

Answer 41

Red-sensitive, green-sensitive and blue-sensitive. They all contain different optimal pigments. When they are stimulated in different proportions you see different colours.

Question 42

Rods are more ..., but cones let you see more ... .

Answer 42

sensitive detail.

Question 43

Are rods or cones very sensitive to light?

Answer 43

Rods.

Question 44

Do rods or cones work well in dim light? Why?

Answer 44

Rods (very sensitive to light). Because many rods join one neurone, so many weak generator potentials combine to reach the threshold and trigger an action potential

Question 45

Do rods or cones work best in bright light? Why?

Answer 45

Cones (less sensitive to light). Because one cone joins one neurone, so it takes more light to reach the threshold and trigger an action potential.

Question 46

Give a definition of visual acuity?

Answer 46

The ability to tell apart points that are close together.

Question 47

Do rods or cones give low visual acuity? Why?

Answer 47

Rods. Because many rods join the same neurone, which means light from two points close together can't be told apart.

Question 48

Do rods or cones give high visual acuity? Why?

Answer 48

Cones. Because cones are close together and one cone joins one neurone. When light from two points hits two cones, two action potentials (one from each cone) go to the brain - so you can distinguish two points that are close together as two separate points.

Question 49

In rods does the brain get separate information about two close points? Regarding visual acuity.

Answer 49

No.

Question 50

In cones does the brain get separate information about two close points? Regarding visual acuity.

Answer 50

Yes.